1. Field of the Invention
The subject matter of the present invention relates to a record and playback system for recording a repetition reduced digital representation of a partially repetitive signal on a data record and for playing back the data record to reconstruct the signal.
2. Description of the Prior Art
Various systems have been suggested for reducing redundant information contained in a periodic partially repetitive signal to produce a modified signal, transmitting the modified signal to a receiver, and then reconstructing the periodic signal from the received modified signal. However, most of these systems are designed to limit the bandwidth of the transmitted signal by spreading the transmission of the lesser amount of information contained in the modified signal for each period over the entire time interval of the period. Due to limitations in such systems, they generally lack the ability to transmit all the non-redundant information from the signal when successive periods of the signal change rapidly and hence contain a large amount of nonredundant information. It is common practice in these systems to simply delete nonredundant information whenever transmission of all such information is impossible. As a consequence, the resulting reconstructed signal is of low quality. In a particular, a reconstructed video signal can end up blurred or otherwise distorted. Furthermore, such systems are not designed to permanently record a data record for later replay.
U.S. Pat. No. 3,571,505 of Mounts exemplifies such bandwidth limited systems. In Mounts, "significant" frame-to-frame changes in video information of a television signal are stored in a transmission buffer memory for transmission to a receiver and subsequent insertion into a frame memory. Reconstruction of the video signal is accomplished using data stored in the frame memory. Bandwidth limitation occurs in Mounts because the amount of frame-to-frame video amplitude change in a word required before a changed word is deemed "significant" varies and depends upon the fullness of the transmission buffer. That is, until a minimum number of words have been stored in the transmission buffer, words will be stored in this buffer even though they have not changed from the corresponding words in the previous frame. The fuller the transmission memory becomes, the greater the required frame-to-frame change in video amplitude of a word before the change is considered "significant." For this reason, when the transmission buffer is almost filled, only words that have changed a large amount will be placed in the buffer. In addition, when the buffer is full, no words, regardless of the degree of change, will be placed in the buffer. Therefore, in Mounts when frames are changing rapidly, nonredundant information from the frames is not transmitted. Furthermore, when frames are changing slowly, even unchanged words are transmitted and occupy bandwidth space.
A second system for reducing redundant information in a transmitted signal is mentioned in the background section of the Mounts patent. In this system, telemetering information is transmitted from a satellite to earth at a fixed rate with each transmitted word apparently having an associated unique address. However, to enable tracking of the satellite, such a system must continuously transmit information whether or not there has been any data changes.
Another form of prior art bandwidth limited system is disclosed in U.S. Pat. Nos. 3,755,624 and 3,758,713 of Sekimoto. In Sekimoto, only "nonredundant" lines of the signal are transmitted. A line may be deemed "nonredundant" and transmitted even though most words in the line have not changed from corresponding previous words. Therefore, unchanged words in such lines will take up space in the transmission bandwidth. The Sekimoto system receives information at a high rate and transmits the nonredundant lines at a lower rate to thereby compress the bandwidth required for transmission of the signal. However, if there are too many frame-to-frame changes in the signal, then all of the changes cannot be transmitted because of the low transmission rate. As a result, Sekimoto does not transmit all of the nonredundant lines when rapid frame-to-frame changes in the signal are occurring. For this reason, the quality of the signal reconstructed from the transmitted information is impaired.
Unlike these systems, the present invention intermittently records a data record with a repetition reduced representation of a partially repetitive signal. Furthermore, this invention is not limited to a fixed bandwidth, but instead can accommodate any rate of data change without deleting nonredundant information from the recording.
Another redundancy reduced record and playback system is disclosed in U.S. Pat. No. 3,924,062 of Broadbent. Broadbent reduces the storage space used on a data record by only recording one entire frame of a plurality of consecutive frames of a television signal. On playback, the recorded frame is repeated a sufficient number of times to substitute for the omitted frames. Like the bandwidth limited systems, Broadbent suffers from the poor quality of the signal on playback because information from the omitted frames has been eliminated.